Exemplary embodiment of the invention relate to an unmanned aircraft, as well as to an operating method therefor.
An unmanned aircraft, also known as a drone or an unmanned aerial vehicle (UAV), is a flying apparatus for unmanned aviation that can be used, for example, for surveillance, exploration, or reconnaissance, as a target drone, for measurement purposes, or even equipped with weapons, especially in combat zones. Drones can be used, for example, for military, secret services, or civilian purposes. A flying drone is unmanned, either automated via a computer program or controlled from the ground via radio signals or via satellite broadcasting. Depending on the application and equipment, drones can bear payloads, such as rockets for a military attack.
In the commonly used terminology, such aircraft are customarily referred to by the abbreviation UAV, which stands for an “unmanned aerial vehicle”. Another abbreviation, UAS, which stands for “unmanned aircraft system”, has also gained currency. The designation encompasses the entire system, constituted of the flying drone, the ground station for takeoff and (where appropriate) landing, and the station for guidance and supervision of the flight.
A comprehensive representation of UASs and different UAVs can be found in Reg Austin's “Unmanned Aircraft Systems—UAVS design, development and deployment”, published by Wiley in 2010. The present disclosure builds upon the knowledge gained in that publication, and the document is hereby incorporated by reference.
German patent document DE 10 2010 021 022 A1 discloses a UAV in the form of a tiltwing aircraft.
UAVs with hybrid systems are known from patent documents U.S. Pat. No. 8,128,019 B2 and EP 2 196 392 A2. These two documents relate to mini-UAVs, which can be brought by foot soldiers into the field and can fly with very low power at low altitude. In such a case, an internal combustion engine is operated at a constant speed; an additional electric motor is variably operated in order to adjust the power in a simple and lightweight configuration.
Larger UAVs having a maximum takeoff weight from about 70 kg to about 1,000 kg are currently operated solely with reciprocating engines, with which petrol engines are generally used. Even larger UAVs generally have gas turbine jet engines in order to be able to generate the requisite power output.
The invention is aimed in particular at such larger UAVs having a maximum takeoff weight from about 70 kg, and exemplary embodiments are directed to an unmanned flying apparatus having a low-cost propulsion that also be used in a very versatile manner for different flight functions.
Exemplary embodiments of the invention are directed to an unmanned aircraft having a propulsion that comprises an internal combustion engine, configured as a diesel and/or kerosene engine, having a charger device for engine charging.
Preferably, the propulsion is a hybrid propulsion which, in addition to the internal combustion engine, comprises an electric motor and an energy storage device for storing electric energy for driving the electric motor.
Preferably the hybrid propulsion comprises a switchable coupling device with which the internal combustion engine and/or the electric motor can be selectively connected to a thrust generator.
Preferably, the internal combustion engine and the electric motor can be selectively operated in parallel or in series.
Preferably, the charging device is designed for multi-stage charging and/or comprises at least a first charger and a second charger, in particular for multi-stage charging.
Preferably, the charging device comprises at least one charger that can be driven by exhaust gas energy.
Preferably, the charging device comprises at least one mechanical charger.
Preferably, the at least one mechanical charger can be driven by an output shaft of the internal combustion engine and/or through an electric motor.
Preferably, the mechanical charger can be driven by the electric motor of the hybrid propulsion.
Preferably, a controller is provided, with which the charger device and/or the hybrid propulsion can be controlled in accordance with various parameters in flight operation.
Preferably, the controller is designed in order to control the charger device and/or the hybrid propulsion, in particular the switching on and off of a first and/or second stage of the engine charging or the switching on and off of the electric motor, in accordance with at least one of the parameters of altitude, angle of a takeoff and/or landing flight to the vertical, desired velocity, allowable heat output, allowable operating noise level, and/or temperature.
Preferably, the internal combustion engine is a rotary piston engine.
Preferably, the aircraft has a maximum takeoff weight of more than 70 kg, and in particular of more than 250 kg.
According to another aspect, the invention provides a method for operating such an unmanned aircraft, the method involving controlling charging of an internal combustion engine of a propulsion of the and/or a cooperation between an internal combustion engine and electric motor of a hybrid propulsion in accordance with at least one of the parameters of altitude, angle of a takeoff and/or landing flight to the vertical, desired velocity, allowable heat output, allowable operating noise level, and/or temperature.
Preferably, upon violation of a predetermined limit value for the at least one parameter, then:                a first charging stage,        a second charging stage,        a mechanical charger,        an electric charger,        a first turbocharger,        a second turbocharger, or        an electric motor in addition to the running internal combustion engine and/or        the internal combustion engine in addition to the running electric motor        is switched on or switched off.        
UAVs are used for various applications in various configurations, for both military and civilian purposes. With regard to energy efficiency, it would be advantageous to have purely electric propulsion. Purely electric propulsion would also be advantageous especially in military operations in terms of the thermal or acoustic signature. In other words, an electric propulsion has an advantage for UAVs in military use in that an especially quiet flight operation and/or a flight operation with low thermal emission is possible, such that the risk of the UAV being detected is reduced.
Currently, however, purely electric propulsion is only suitable for low power and low flight times. For example, a purely electric propulsion could be feasible for tactical UAVs with a maximum takeoff weight of up to about 70 kg in flight times between 20 minutes and at most three hours. Typical propulsion power would then be between 2 and 20 kW. There is then, however, a problem in the storage density of contemporary batteries.
To be able to take advantage of an electric propulsion also for larger UAVs, and also for higher flight altitudes and longer distances—especially for UAVs of the medium-altitude long-endurance (MALE) class, or the high-altitude long-endurance (HALE) class, the invention provides for the use of internal combustion engines, which are diesel- or kerosene-drive and have a charging system.
Especially preferably, these internal combustion engines are a part of a hybrid propulsion; in particular, a diesel-electric hybrid propulsion is provided.
Diesel and kerosene engines can be used universally, e.g., as propulsion for maritime UAVs. The corresponding engines have a lower fuel consumption than petrol engines or gas turbines, and also have a better partial load response.
For the purpose of optimizing energy and system technology, charging through a charger device is provided according to the invention.
If the exhaust gas energy of the internal combustion engines is used here for charging, such as with the exhaust gas energy of diesel engines, then the thermal signature can thereby be considerably reduced.
Preferably, such a charged diesel or kerosene internal combustion engine is combined with electrical components in a power train for UAVs. This offers, in particular, the following advantages:
For example, purely electric operation is possible in the emission region. The landing approach can be carried out using the internal combustion engine, where a purely or mostly electric operation takes place in the emission region in order to reduce the thermal and acoustic signature and thus increase the safety of the aircraft.
It is possible to have a boost operation by connecting an electric motor into the mechanical drive train. Such a boost operation can be used, for example, for the takeoff and/or landing phase in critical environmental conditions, for escaping, or for other situations where unusually high power is needed.
Such a propulsion can be used for all conceivable configurations of the UAV. The UAV can have, for example, a helicopter configuration, an A/C configuration, a tiltwing configuration, and/or a tiltrotor configuration.
In particular, according to one embodiment of the invention, UAVs can be propelled with propeller propulsion and/or impeller propulsion or with rotors of the performance class 30 kW to 400 kW per individual internal combustion engine. At requisite higher power, it would be possible to use, for example, a plurality of internal combustion engines. It would be particularly advantageous to take diesel/kerosene/rotary piston engines into consideration.
Such a rotary piston engine is very compact and, even when used with diesel or kerosene, is relatively lightweight. In addition, a rotary piston engine can easily be used at a plurality of power stages. For a lower power stage, it would be possible to use, for example, a single-rotor rotary piston engine, while at high power levels, another rotor would come into use, and so forth.
A particularly preferred embodiment relates to the combination of one such internal combustion engine with one electrical motor and one electric energy storage device into a hybrid propulsion, which is preferably provided as a parallel hybrid, meaning the provision of various charging concepts for the internal combustion engine.
Preferably, a UAV is provided with “heavy fuel” fuel operation and with charging. “Heavy fuel” refers in the USA in particular to diesel and/or kerosene propulsion.
Charged diesel engines are, of course, well known in the automotive industry. One example of a well-known charged diesel engine is the three-cylinder turbodiesel “Smart” car engine, which is also commercially available as an individual engine. In the present invention, a charged diesel engine or a charged kerosene engine is used for an unmanned aircraft. This is of particular interest for maritime applications of UAVs.
The charging of the internal combustion engine is especially advantageous. For example, charging is provided using the exhaust gas energy. In particular, chargers coupled to exhaust gas turbines (“turbochargers”) are used here. In particular, use is made of the exhaust gas energy in two stages, through a series of connected exhaust gas turbines. Using the exhaust gas energy makes it possible to reduce the exhaust gas temperature. This lowers the signature for IR detection of the UAVs.
Further advantages of engines operating with diesel or kerosene are better efficiency and better partial load response as compared to petrol engines or gas turbines; in addition, such engines are more durable. Diesel engines output their rated power at a lower rotational speed.
More preferably, at least one first charger and one second charger are provided, in order to enable at least one two-stage charging.
The internal combustion engine can operate without charging for higher altitudes and lower power. For slightly higher power, a first stage of charging is switched on. For even higher power, the second stage can then be triggered. Of particular interest is two-stage charging with further usage of the exhaust gas energy. Such two-stage charging is interesting for higher altitudes above around 4,000 m and can be used even at altitudes of about 10,000 m to 12,000 m.
Another interesting concept is the mechanical charging. It is thus preferable for the internal combustion engine to comprise at least one mechanical charger as a charger. The advantage of mechanical charging is that the motor does not need to work against the exhaust gas pressure. Preferably, the mechanical charging can be decoupled. The mechanical charger can be drive, for example, via a drive shaft of the internal combustion engine and/or via an electric drive. The electric motor of the hybrid propulsion is particularly preferably used as the electric drive.
Thus, it is conceivable to have multi-stage charging with or without the use of exhaust gas energy, by the use of mechanical energy from the internal combustion engine or from the electric drive.
It is particularly preferable to provide a controller which controls the different manners of propulsion (electric motor and/or internal combustion engine) and/or the different charging systems depending on different parameters in flight operation of the UAV.
Possible parameters therefor are different altitudes. These can be detected, for example, via a pressure sensor. In such an embodiment of the invention, the UAV comprises a pressure sensor producing signals that are used to control the propulsion. Other examples of possible parameters are altitude and/or fast flight. Another parameter may be the power for takeoff and/or landing operations. With such a propulsion concept, both UAVs of the MALE class and UAVs of the HALE class can be operated with great functional versatility and a wide range of possible applications.
According to another aspect, the invention provides a UAV having a hybrid propulsion in which the UAV is operated as a mobile power supply unit after landing. The UAV preferably flies to the desired location and, once there, is readily available, in contrast to ground-based emergency generators. Through the increased application flexibility, the UAV can fly in particular to locations that are difficult or even impossible to reach by land and then ensure power there. The internal combustion engine, which drives the generator to provide the desired power, serves as the primary energy supply. In another embodiment, the electric energy storage device can be omitted so as to economize on weight. The UAV is as described above and below.